Updated FAQ (markdown)

FAQ.md

@@ -33,6 +33,23 @@ AVPlayer is a system player component delivered by Apple. It provides best effic
 
 [mpv](https://mpv.io/) is an open source, free media player that offers much winder range of supported formats and is capable of playing 4K+ videos, using hardware decoding wherever possible. It uses custom playback controls. Due to implementation limitations it is not possible to start PiP or AirPlay from MPV directly, however app allows seamless switch to AVPlayer for opening PiP.
 
+6. **I am using Invidious and thumbnails don't load for me in the app, although it works fine in Invidious front-end in the browser**
+
+Most probably your instance is not properly configured.
+
+Go to address:
+https://your.instance.com/api/v1/videos/rr2XfL_df3o
+and check what thumbnails URLs are being generated by the API (_videoThumbnails_ key).
+It should give you URL matching scheme, without port if it is not necessary and the URL should be direct to the thumbnail file, it should not be redirecting.
+
+If it is not the case, check your Invidious instance settings, you should set the following values when using with https:
+
+```
+domain: your.instance.com
+external_port: 443
+```
+
+
 ## Platform specific
 ### macOS
 1. **Is Yattee ever going to be available via the Mac App Store?**